In case of a header with a valu of tpe System.Guid, the untyped value…

… cannot cast to a string. When resubmitting a message (for example from a deadletterqueue to the original queue) the heeaders of type Guid are ignored.

Helpers/ConversionHelper.cs

@@ -123,7 +123,7 @@ public static object MapStringTypeToCLRType(string type, object value)
                 case "Decimal":
                     return Convert.ChangeType(value, typeof(decimal));
                 case "Guid":
-                    return new Guid(value as string);
+                    return new Guid(value.ToString());
             }
             throw new NotSupportedException(string.Format(TypeNotSupported, type));
         }